Response to selection for lower initial rate of dry matter disappearance in the development of a bloat-tolerant non-dormant alfalfa population

Frothy bloat is a digestive dysfunction of rumiant animals associated with the consumption of fresh and highly digestible alfalfa under direct grazing. It is related to the very rapid exposure of chloroplast fragments and soluble proteins from mesophyll cells to the action of the rumen microorganisms shortly after feeding. The selection for lower initial rate of dry matter disappearance (IRDMD) has been proposed to develop alfalfa cultivars with reduced bloating potential. This paper summarizes the results of a breeding program initiated in 1991 by INTA-Produsem, Argentina. After two cycles of phenotypic and genotypic recurrent selection for lower IRDMD by using a modified in situ nylon bag technique, C-2 (2^nd selection cycle) population exhibited a general reduction relative to the original (C-O) population. When compared to C-O, C-1 (1^st selection cycle) population exhibited higher fiber (ADF and NDF) content, which was consequently reflected in lower Leaf / Stem ratio, Crude Protein, and Relative Feed Value for the selected population. However, the actual detrimental effect of this lower forage quality on animal production appears to be unimportant so far. Reduction in average IRDMD did not narrow down the variability in the selected populations, supporting the possibility of further selection if necessary.